This fuse is used for capacitor banks with a large number of parallel capacitors. It can be used on applications with essentially infinite parallel stored energy, as long as sufficient back voltage can be developed to force the current to extinguish.
For high voltage capacitor fuses, this is generally defined as 8.3, 15.5 or 23 kV, the distribution system maximum voltages. Other voltage ratings may be available for special applications. When a capacitor fails, the energy stored in its series group of capacitors is available to dump into the combination of the failed capacitor and fuse.
Most capacitor fuses have a maximum power frequency fault current that they can interrupt. These currents may be different for inductive and capacitively limited faults. For ungrounded or multi-series group banks, the faults are capacitive limited.
The capacitor must be able to absorb this energy with a low probability of case rupture. Fuses are usually applied with some continuous current margin. The margin is typically in the range of 1.3 to 1.65 per unit. This margin is called the fusing factor.
The fuse protecting the capacitor is chosen such that its continuous current capability is equal to or greater than 135% of rated capacitor current for grounded-wye connected racks, and 125% for ungrounded-wye racks. This overrating includes the effects of overvoltage, capacitor tolerance, and harmonics.
Eaton’s Cooper PowerE series bus-mounted expulsion-type capacitor fuse provides highly reliable, economical protection for capacitor banks where medium-energy-interrupting ability is required. See Table 1 for electrical ratings. The fuse tube is constructed of bone-grade fibre overwrapped with epoxy-bonded filament-wound fiberglass.